Acidic gas-absorbing liquid and acidic gas reduction method

Abstract

Provided is an acid gas-absorbing liquid containing: an oxygen-containing polymer; an amine compound having a pKa of 7 or more; and an antioxidant, wherein the antioxidant content is 0.05-20.0 mass%.

Description

Acid gas absorption solution and method for reducing acid gas

[0001] This invention relates to an acidic gas absorption liquid and a method for reducing acidic gases using the same.

[0002] A known method for recovering acidic gases, such as carbon dioxide, from a gas is to use an acidic gas absorbent (hereinafter simply referred to as "absorbent") containing an amine compound and an organic solvent to absorb and separate the acidic gas, and then recover the absorbed acidic gas by desorption from the absorbent by heating. Such an absorbent utilizes the reversible reaction of amine salt formation and regeneration by the amine compound, and is also called a chemical absorbent.

[0003] In the above-mentioned methods for recovering acidic gases, various methods have been proposed to reduce the energy required for heating when desorbing the acidic gas from the absorbent solution, from the viewpoint of energy conservation. For example, Patent Document 1 proposes a method using an absorbent solution containing an amine compound and an organic solvent whose solubility parameter difference with the amine compound is within a predetermined range. This method utilizes the fact that by selecting a combination of the amine compound and alcohols such as 1-butanol and 1-pentanol, or ethers such as diethylene glycol diethyl ether, the absorbent solution that has absorbed the acidic gas will undergo phase separation into a phase with a high acidic gas content and a phase with a low acidic gas content. By selectively heating the phase with a high acidic gas content and performing an acidic gas desorption treatment, it is possible to reduce the energy required for recovering the acidic gas compared to when the entire absorbent solution is subjected to the acidic gas desorption treatment.

[0004] Japanese Patent Publication No. 2017-113672

[0005] Incidentally, exhaust gases from thermal power plants and various industrial processes often contain water vapor (moisture). Acidic gas absorbents used in such processes absorb carbon dioxide from exhaust gases containing moisture, and then undergo heating to decarbonize the carbon dioxide and separate and remove the moisture, thereby regenerating the absorbent.

[0006] The absorbent liquid described in Patent Document 1 is susceptible to deterioration due to oxidation by oxygen and nitrogen oxides contained in the exhaust gas that comes into contact with it. Furthermore, when the absorbent liquid is reused after absorbing carbon dioxide, heating it to a high temperature (e.g., 100°C) for regeneration can sometimes worsen its carbon dioxide absorption capacity.

[0007] The present invention was made to solve these problems and aims to provide an acidic gas absorbent and an acidic gas reduction method that have good carbon dioxide absorption capacity even after being exposed to an oxidizing atmosphere or high-temperature environment.

[0008] This invention is based on the discovery that an acidic gas absorption solution containing an oxygen-containing polymer, an amine compound having a predetermined pKa, and a predetermined amount of antioxidant maintains good carbon dioxide absorption capacity even after being exposed to an oxidizing atmosphere or high-temperature environment.

[0009] The present invention provides the following means: [1] An acidic gas absorbent comprising an oxygen-containing polymer, an amine compound having a pKa of 7 or higher, and an antioxidant, wherein the antioxidant content is 0.05 to 20.0% by mass. [2] The acidic gas absorbent according to [1], wherein the oxygen-containing polymer content is 5.0 to 90.0% by mass. [3] The acidic gas absorbent according to [1] or [2], wherein the amine compound content is 10.0 to 95.0% by mass. [4] The acidic gas absorbent according to [1], wherein the amine compound is a compound having one primary amino group or a secondary amino group. [5] The acidic gas absorbent according to any one of [1] to [4], wherein the antioxidant is at least one selected from the group consisting of phenolic antioxidants, sulfur-based antioxidants, amine-based antioxidants having a pKa of less than 7, and phosphorus-based antioxidants. [6] The acidic gas absorbent according to [5], wherein the antioxidant comprises at least one selected from the group consisting of the phenolic antioxidant and the amine antioxidant, and at least one selected from the group consisting of the sulfuric antioxidant and the phosphorusic antioxidant. [7] The acidic gas absorbent according to [5], wherein the antioxidant comprises the sulfuric antioxidant. [8] The acidic gas absorbent according to any of [1] to [7], wherein the oxygen-containing polymer has at least one group selected from the group consisting of an oxyalkylene group, a carbonate group, and an ester group. [9] The acidic gas absorbent according to any of [1] to [8], for use in an acidic gas recovery and separation process.

[10] An acidic gas reduction method comprising contacting the acidic gas absorbent according to any of [1] to [9] with a gas containing carbon dioxide to reduce the carbon dioxide in the gas.

[0010] The present invention provides an acidic gas absorbent and an acidic gas reduction method that maintain good carbon dioxide absorption capacity even after exposure to an oxidizing atmosphere or high-temperature environment.

[0011] The definitions and significance of terms and notations used in this specification are given below. Numerical ranges expressed using "~" indicate that the numbers before and after "~" are the lower and upper limits, respectively. The number-average molecular weight (Mn) of oxygen-containing polymers is the molecular weight determined by gel permeation chromatography (GPC) using polystyrene as the standard substance. pKa is the acid dissociation constant, and is the value described in the literature (CAS SciFinder), but it can also be calculated by measurement using the neutralization titration method.

[0012] [Acidic Gas Absorbent Solution] The acidic gas absorbent solution of the present invention contains an oxygen-containing polymer, an amine compound with a pKa of 7 or higher, and an antioxidant. Furthermore, the content of the antioxidant in the acidic gas absorbent solution of the present invention is 0.05 to 20.0% by mass.

[0013] The acidic gas is a gas containing carbon dioxide, and may also contain other acidic gases such as hydrogen sulfide or sulfur dioxide. The acidic gas absorbent liquid of this embodiment (hereinafter referred to as "this embodiment") can reversibly absorb and desorb carbon dioxide from acidic gases, and can be regenerated and reused. The following explanation will use the case where the acidic gas absorbed by the acidic gas absorbent liquid is carbon dioxide as an example.

[0014] The acidic gas absorbent of this embodiment contains an oxygen-containing polymer, an amine compound having a predetermined pKa, and a predetermined amount of antioxidant. Conventionally, when an acidic gas absorbent is exposed to an oxidizing atmosphere or high-temperature environment, the concentration of the amine compound may decrease, and the carbon dioxide absorption capacity may deteriorate. In contrast, the above-mentioned acidic gas absorbent contains a predetermined antioxidant, which suppresses the reduction in the concentration of the amine compound contained in the acidic gas absorbent even when exposed to an oxidizing atmosphere or high-temperature environment, and thus maintains good carbon dioxide absorption capacity.

[0015] (Oxygen-containing polymer) The oxygen-containing polymer contained in the acidic gas absorbent preferably has at least one group selected from the group consisting of oxyalkylene groups, carbonate groups, and ester groups, and more preferably has an oxyalkylene group. With such an oxygen-containing polymer, the ether bond, ester bond, or carbonate bond site of the oxygen-containing polymer has a high affinity for carbon dioxide, which makes it easier to improve absorption performance.

[0016] The oxygen-containing polymer preferably has a group represented by -OR at its terminal end. In -OR, R is a hydrogen atom or a carbon-containing group having 1 to 4 carbon atoms. The carbon-containing group may be linear or branched, may have an unsaturated bond, and may contain at least one of a nitrogen atom and an oxygen atom, preferably a hydrogen atom or an alkyl group. The presence of an oxygen-containing terminal group improves the diffusibility of carbon dioxide and thus the absorption performance of the oxygen-containing polymer.

[0017] Examples of oxygen-containing polymers include polyethers, polycarbonates, and polyesters. Among these, oxygen-containing polymers in which the R in the terminal -OR is a hydrogen atom, i.e., have a hydroxyl group at the terminal, include polyether monools, polyether polyols, polyester polyols, polycarbonate polyols, and polyether polycarbonate polyols. Oxygen-containing polymers in which a group other than a hydroxyl group represented by -OR is introduced at the terminal will be described later. Oxygen-containing polymers may be used alone or in combination of two or more types.

[0018] <Polyether Monools> Polyether monools are preferably obtained by addition polymerization of an alkylene oxide to an initiator having one active hydrogen atom per molecule. Addition polymerization can be carried out by known methods in the presence of a catalyst.

[0019] The initiator is preferably a compound having one hydroxyl group in one molecule, and examples of monohydric alcohols include methanol, ethanol, 2-propanol, n-butanol, tert-butanol, allyl alcohol, isobutanol, 2-ethylhexanol, decyl alcohol, lauryl alcohol, tridecanol, cetyl alcohol, stearyl alcohol, oleyl alcohol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monoisobutyl ether, ethylene glycol mono-tert-butyl ether, ethylene glycol monohexyl ether, ethylene glycol monophenyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monobenzyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, and tetraethylene glycol monobutyl ether. The initiator may be used alone or in combination of two or more.

[0020] The alkylene oxide preferably has 2 to 20 carbon atoms, more preferably 2 to 10 carbon atoms, and even more preferably 3 to 8 carbon atoms. Examples of alkylene oxides include propylene oxide, 1,2-butylene oxide, 2,3-butylene oxide, tetramethylene oxide (tetrahydrofuran), and α-olefin oxides having 5 to 20 carbon atoms. Of these, propylene oxide is preferred. The alkylene oxide may be used alone or in combination of two or more types.

[0021] Known catalysts can be used, including, for example, alkaline catalysts such as potassium hydroxide, transition metal compound-porphyrin complex catalysts such as complexes obtained by reacting organoaluminum compounds with porphyrin, complex metal cyanide complex catalysts such as zinc hexacyanocobaltate complexes with tert-butanol as a ligand, and catalysts consisting of phosphazene compounds. The catalyst may be used alone or in combination of two or more.

[0022] <Polyether Polyols> Polyether polyols are preferably obtained by addition polymerization of alkylene oxide to an initiator having two or more active hydrogen atoms in one molecule.

[0023] The initiator is preferably a compound having two or more hydroxyl groups in one molecule, such as dihydric alcohols like ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, tripylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,6-hexanediol, 1,4-cyclohexanediol, bisphenol A, bisphenol F, bisphenol S, and resorcinol; and trihydric or higher alcohols like glycerin, diglycerin, trimethylolpropane, pentaerythritol, dipentaerythritol, tripentaerythritol glucose, sorbitol, dextrose, fructose, sucrose, methyl glucoside, trehalose, novolac, resol, and castor oil. Water can also be used as an initiator. Of these, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, glycerin, trimethylolpropane, pentaerythritol, and sorbitol are preferred. The initiator may be used alone or in combination of two or more.

[0024] Specific examples of alkylene oxides include those similar to the alkylene oxides used as raw materials for the synthesis of polyether monools described above. Addition polymerization can also be carried out in the same manner as the synthesis of polyether monools described above.

[0025] Specific examples of polyether polyols include polyethylene glycol, polypropylene glycol, polyoxyethylene polyoxypropylene glycol, polytetramethylene ether glycol, and addition polymers of polytetramethylene ether glycol and alkylene oxide.

[0026] Polyether polyols having a repeating unit with 3 or more carbon atoms are preferred, since polyether polyols of this type readily afford an absorbent liquid with high hydrophobicity and suppressed latent heat of vaporization. In particular, polypropylene glycol or polyoxyethylene polyoxypropylene glycol is more preferred, because these have reduced crystallinity and good fluidity even at low temperatures. It should be noted that when polyether polyol is oxidized, the ether oxygen cleaves and deteriorates. Therefore, addition of an antioxidant is effective for any polyether polyol to suppress oxidative deterioration.

[0027] <Polyester polyol> The polyester polyol is preferably a reaction product of an esterification reaction between a dibasic acid and a polyhydric alcohol, or a transesterification reaction between a dialkyl dibasic acid ester and a polyhydric alcohol. The esterification reaction or transesterification reaction can be performed by a known method in the presence of a catalyst.

[0028] Examples of the dibasic acid include aliphatic dibasic acids such as succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, brassylic acid, and dimer acid; alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid; and aromatic dibasic acids such as phthalic acid, isophthalic acid, terephthalic acid, and naphthalenedicarboxylic acid. Examples of the dialkyl dibasic acid ester include dimethyl esters, diethyl esters, dipropyl esters, and dibutyl esters of the dibasic acids exemplified above. One type of dibasic acid may be used alone, or two or more types may be used in combination.

[0029] Examples of polyhydric alcohols include diols such as ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, triethylene glycol, tripropylene glycol, neopentyl glycol, 1,4-butanediol, and 1,6-hexanediol; and trihydric or higher alcohols such as glycerin, trimethylolpropane, trimethylolethane, pentaerythritol, sorbitol, and sucrose. Polyhydric alcohols may be used individually or in combination of two or more.

[0030] Examples of catalysts include titanium compounds such as tetrabutyl titanate, tetraisopropyl titanate, tetra-2-ethylhexyl titanate, and titanium acetylacetonate; tin compounds such as dibutyltin oxide, methylphenyltin oxide, and hexaethyltin oxide; and magnesium compounds such as magnesium carbonate, magnesium oxide, and magnesium alkoxide. The catalyst may be used alone or in combination of two or more types.

[0031] <Polycarbonate Polyols> Examples of polycarbonate polyols include polycondensates of polyhydric alcohols and carbonate compounds, and polycondensates of polyhydric alcohols and cyclic esters and carbonate compounds. Polycarbonate polyols can be synthesized by known methods.

[0032] Examples of polyhydric alcohols include ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, 1,12-dodecanediol, 1,13-tridecanediol, and 1,14-tetradecanediol. 1,16-Hexadecanediol, 1,18-Octadecanediol, 1,20-Eicosanediol, 2-Methyl-1,8-Octanediol, 2,2-Dimethyl-1,3-Propanediol, 2-Ethyl-1,3-Hexanediol, 2-Ethyl-1,6-Hexanediol, 2-Methyl-1,4-Butanediol, 2-Methyl-1,3-Propanediol, 3-Methyl-1,5-Pentanediol, 2 Examples include aliphatic diols such as ,4-dimethyl-1,5-pentanediol and 2,4-diethyl-1,5-pentanediol; alicyclic diols such as 1,3-cyclohexanediol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, isosorbide, 2-bis(4-hydroxycyclohexyl)-propane, 2,7-norbornanediol, 2,3-norbornanediol, tetrahydrofuran-2,2-dimethanol, and 2,5-bis(hydroxymethyl)-1,4-dioxane; and aromatic diols such as 5,5-bis(hydroxymethyl)-2-phenyl-1,3-dioxane, p-xylene glycol, p-tetrachlorooxylendiol, 1,4-bis(hydroxyethoxy)benzene, and 2,2-bis[(4-hydroxyethoxy)phenyl]propane. Polyhydric alcohols may be used alone or in combination of two or more.

[0033] Examples of carbonate compounds include dimethyl carbonate, diethyl carbonate, dipropyl carbonate, dibutyl carbonate, diphenyl carbonate, ethylene carbonate, trimethylene carbonate, propylene carbonate, 1,2-butylene carbonate, and neopentylene carbonate. A single carbonate compound may be used, or two or more may be used in combination.

[0034] Examples of cyclic esters include ε-caprolactone, β-propiolactone, β-methyl-β-propiolactone, δ-valerolactone, glycolides, and lactides. Cyclic esters may be used individually or in combination of two or more.

[0035] <Polyether Polycarbonate Polyols> Examples of polyether polycarbonate polyols include polycondensates of polyether polyols and carbonate compounds. They may also be copolymers of diol compounds different from polyether polyols. Polyether polycarbonate polyols can be synthesized by known methods.

[0036] Specific examples of polyether polyols include the polyether polyols mentioned above, and specific examples of carbonate compounds include those similar to the carbonate compounds that are used as raw materials for the synthesis of polycarbonate polyols mentioned above.

[0037] <Oxygen-containing polymers in which a group other than a hydroxyl group represented by -OR is introduced at the end of the oxygen-containing polymer> Examples of oxygen-containing polymers in which a group other than a hydroxyl group represented by -OR is introduced at the end of the oxygen-containing polymer include polyoxyalkylene dimethyl ether, polyoxyalkylene ethyl ether, polyoxyalkylene propyl ether, polyoxyalkylene isopropyl ether, polyoxyalkylene allyl ether, polyoxyalkylene butyl ether, polyoxyalkylene sec-butyl ether, polyoxyalkylene tert-butyl ether, polyoxyalkylene pentyl ether, polyoxyalkylene hexyl ether, polyoxyalkylene heptyl ether, polyoxyalkylene octyl ether, polyoxyalkylene (2-ethylhexyl) ether, polyoxyalkylene ethyl methyl ether, polyoxyalkylene propyl methyl ether, polyoxyalkylene isopropyl methyl ether, polyoxyalkylene butyl methyl ether, polyoxyalkyl Examples include polyoxyalkylene sec-butyl methyl ether, polyoxyalkylene tert-butyl methyl ether, polyoxyalkylene pentyl methyl ether, polyoxyalkylene hexyl methyl ether, polyoxyalkylene octyl methyl ether, polyoxyalkylene 2-ethylhexyl methyl ether, polyoxyalkylene methyl allyl ether, polyoxyalkylene ethyl allyl ether, polyoxyalkylene propyl allyl ether, polyoxyalkylene isopropyl allyl ether, polyoxyalkylene butyl allyl ether, polyoxyalkylene sec-butyl allyl ether, polyoxyalkylene tert-butyl allyl ether, polyoxyalkylene pentyl allyl ether, polyoxyalkylene hexyl allyl ether, polyoxyalkylene heptyl allyl ether, polyoxyalkylene octyl allyl ether, and polyoxyalkylene 2-ethylhexyl allyl ether.Of these, polyoxyalkylene dimethyl ether, polyoxyalkylene diallyl ether, polyoxyalkylene ethyl methyl ether, polyoxyalkylene propyl methyl ether, polyoxyalkylene isopropyl methyl ether, polyoxyalkylene butyl methyl ether, polyoxyalkylene sec-butyl methyl ether, polyoxyalkylene tert-butyl methyl ether, polyoxyalkylene pentyl methyl ether, polyoxyalkylene hexyl methyl ether, polyoxyalkylene heptyl methyl ether, polyoxyalkylene octyl methyl ether, polyoxyalkylene 2-ethylhexyl methyl ether, polyoxyalkylene methyl allyl ether, polyoxyalkylene ethyl allyl ether, polyoxyalkyl Chelenpropyl allyl ether, polyoxyalkylene isopropyl allyl ether, polyoxyalkylene butyl allyl ether, polyoxyalkylene sec-butyl allyl ether, polyoxyalkylene tert-butyl allyl ether, polyoxyalkylene pentyl allyl ether, polyoxyalkylene hexyl allyl ether, polyoxyalkylene heptyl allyl ether, polyoxyalkylene octyl allyl ether, and polyoxyalkylene 2-ethylhexyl allyl ether are preferred, polyoxyalkylene dimethyl ether, polyoxyalkylene butyl methyl ether, and polyoxyalkylene 2-ethylhexyl methyl ether are more preferred, and polypropylene glycol dimethyl ether, polypropylene glycol butyl methyl ether, and polypropylene glycol monomethyl ether are even more preferred.

[0038] Furthermore, when replacing the terminal hydroxyl groups of the oxygen-containing polymer described above to convert it into an oxygen-containing polymer in which a group other than a hydroxyl group represented by -OR is introduced at the terminal, the terminal hydroxyl groups can be replaced by known methods such as alkoxylation, esterification, or urethaneization. From the viewpoint of achieving a viscosity that allows for uniform mixing with amine compounds during the preparation of the absorbent solution, alkoxylation of the terminal is preferable.

[0039] Alkoxylation of the terminal hydroxyl groups of oxygen-containing polymers can be performed using, for example, organic halogen compounds such as alkyl halides. Examples of organic halogen compounds include organic chlorine compounds such as methyl chloride, ethyl chloride, vinyl chloride, n-propyl chloride, isopropyl chloride, allyl chloride, n-butyl chloride, isobutyl chloride, sec-butyl chloride, tert-butyl chloride, 2-chloroethylmethyl ether, 2-chloroethylethyl ether, 2-chloroethylpropyl ether, and 2-chloroethylbutyl ether; methyl bromide, ethyl bromide, vinyl bromide, n-propyl bromide, isopropyl bromide, allyl bromide, n-butyl bromide, and Examples of organic bromine compounds include isobutyl iodide, sec-butyl bromide, tert-butyl bromide, 2-bromoethylmethyl ether, 2-bromoethylethyl ether, 2-bromoethylpropyl ether, and 2-bromoethylbutyl ether; and organic iodine compounds such as methyl iodide, ethyl iodide, vinyl iodide, n-propyl iodide, isopropyl iodide, allyl iodide, n-butyl iodide, isobutyl iodide, sec-butyl iodide, tert-butyl iodide, and 2-iodoethylmethyl ether. Of these, methyl chloride, allyl chloride, methyl bromide, allyl bromide, methyl iodide, and allyl iodide are preferred from the viewpoint of efficiently converting hydroxyl groups.

[0040] <Number-average molecular weight> The number-average molecular weight (Mn) of the oxygen-containing polymer is preferably 100 to 20,000, more preferably 200 or more, even more preferably 250 or more, even more preferably 10,000 or less, even more preferably 5,000 or less, and particularly preferably 2,000 or less. When Mn is 100 or more, the boiling point of the oxygen-containing polymer tends to be high, and the absorption solution is less likely to be reduced in volume due to volatilization during heating. Also, when Mn is 20,000 or less, the viscosity tends to be such that it is easy to uniformly mix with the amine compound during the preparation of the absorption solution.

[0041] (Amine Compounds) Amine compounds absorb carbon dioxide well, so there are no particular restrictions as long as their pKa is 7 or higher, but a pKa of 8 or higher is preferred, and 8.5 or higher is more preferred. Solubility parameter of amine compounds (δ ａ ) 13.0-25.5 (MPa)１／２ Preferably, and more preferably, 15.0 to 25.0 (MPa) １／２ More preferably 16.0 to 24.0 (MPa) １／２ δ ａ If the above range is present, carbon dioxide is easily absorbed by the absorbent solution. Note that if there are two or more amine compounds in the absorbent solution, δ ａ This is the δ of various amine compounds ａ This is the average volume.

[0042] As for the amine compound, primary amines and secondary amines are preferred from the viewpoint of their tendency to be highly reactive with carbon dioxide, and alkylamines with 2 to 15 carbon atoms and amines having an aromatic ring with 7 to 14 carbon atoms are preferred from the viewpoint of having a viscosity that allows for uniform mixing with the oxygen-containing polymer during the preparation of the absorbent solution.

[0043] If an amine compound has multiple primary or secondary amino groups that can act as reaction sites, the absorbent solution tends to thicken after absorbing carbon dioxide due to intermolecular interactions of the amine compound. For this reason, it is preferable that the amine compound has only one primary or secondary amino group. The amine compound may also have a tertiary amino group.

[0044] Specific examples of amine compounds include butylamine, dibutylamine (DBA), diamylamine (DAA), dihexylamine (DHA), dicyclohexylamine, 2-ethylhexylamine (2EHA), 2-(diethylamino)ethylamine, 3-(diethylamino)propylamine, 3-(dibutylamino)propylamine (DBAPA), di-(2-ethylhexyl)amine, 3,3-iminobis(N,N-dimethylpropylamine), monoethanolamine, diethanolamine, triethanolamine, and triethanolamine. Examples include tanolamine, 2-(ethylamino)ethanol, 2-(butylamino)ethanol (BAE), 2-isopropylaminoethanol, diglycolamine, benzylamine, N-methylbenzylamine (BMA), N-ethylbenzylamine, N-isopropylbenzylamine, and dibenzylamine (DBZA). DBAPA, DBA, DAA, DHA, BAE, DBZA, BMA, or 2EHA are preferred in terms of having good carbon dioxide absorption capacity and good fluidity after carbon dioxide absorption.

[0045] (Antioxidant) There are no particular restrictions on the antioxidant, but examples include phenolic antioxidants, sulfur-based antioxidants, amine-based antioxidants with a pKa of less than 7, and phosphorus-based antioxidants. Since antioxidants tend to maintain good carbon dioxide absorption capacity of the absorbent even after exposure to an oxidizing atmosphere or heating environment, at least one selected from the group consisting of amine-based antioxidants with a pKa of less than 7 and phosphorus-based antioxidants is preferred.

[0046] The antioxidant may be used alone or in combination of two or more. When two or more are used in combination, it is preferable to include at least one selected from the group consisting of amine-based antioxidants and phenol-based antioxidants having a pKa of less than 7, and at least one selected from the group consisting of sulfur-based antioxidants and phosphorus-based antioxidants. It is also preferable for the antioxidant to include a sulfur-based antioxidant.

[0047] Amine-based antioxidants and phenol-based antioxidants trap radicals more easily than the amine compounds mentioned above. Therefore, amine-based and phenol-based antioxidants primarily play a role in trapping radicals generated in carbon dioxide absorption systems, thereby suppressing oxidative degradation of oxygen-containing polymers and amine compounds with a pKa of 7 or higher. Sulfur-based and phosphorus-based antioxidants primarily play a role in regenerating amine-based and phenol-based antioxidants and degraded amine compounds with a pKa of 7 or higher that have lost their carbon dioxide absorption capacity due to reaction with radicals. Therefore, it is believed that by using at least one selected from the group consisting of amine-based and phenol-based antioxidants in combination with at least one selected from the group consisting of sulfur-based and phosphorus-based antioxidants, the lifespan of antioxidants with high radical-trapping function is extended, resulting in the expression of higher antioxidant function.

[0048] <Phenol-based antioxidants> Examples of phenol-based antioxidants include tetrakis(methylene-3-(3',5'-di-tert-butyl-4'-hydroxyphenyl)propionate)methane, octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, octyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, 2,6-dimethylphenol, 2,6-diethyl paracresol, and 2,6-di-tert-butyl paracresol. From the viewpoint of the antioxidant being less volatile, tetrakis(methylene-3-(3',5'-di-tert-butyl-4'-hydroxyphenyl)propionate)methane and octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate are preferred as phenol-based antioxidants.

[0049] <Sulfur-based antioxidants> Examples of sulfur-based antioxidants include bismuthiol, dioctadecyl-3,3'thiodipropionate, 2-mercapto-1-methylimidazole, 2-mercapto-5-methylbenzimidazole, β-mercaptopropionic acid, 2,2-thiodiethanol, 2-mercaptobenzimidazole, 2-mercapto-4-methylimidazole, 2-mercaptobenzuthiazole, 2-mercaptobenzoxazole, 4,6-bis(octathiomethyl)-o-cresol, and trilauryltrithiophosphite. From the viewpoint of the antioxidant being less volatile, dioctadecyl-3,3'thiodipropionate, 4,6-bis(octathiomethyl)-o-cresol, and trilauryltrithiophosphite are preferred as sulfur-based antioxidants.

[0050] <Amine-based antioxidants with a pKa of less than 7> Amine compounds with a pKa of 7 or higher are basic and therefore react with carbon dioxide, giving them the ability to absorb carbon dioxide. On the other hand, amine compounds with a pKa of less than 7 do not react with carbon dioxide and therefore do not have carbon dioxide absorption capabilities. However, they can be used as antioxidants because they act as traps for oxygen radicals that promote oxidative degradation such as the decomposition of oxygen-containing polymers.

[0051] Examples of amine-based antioxidants with a pKa of less than 7 include 4,4'-dimethyldiphenylamine, 4,4'-di-tert-butyldiphenylamine, 4,4'-dioctyldiphenylamine, 2,4,6-trimethylaniline, octylated diphenylamine, and 4,4'-bis(α,α-dimethylbenzyl)diphenylamine. From the viewpoint of the antioxidant being less volatile, 4,4'-dioctyldiphenylamine, octylated diphenylamine, and 4,4'-bis(α,α-dimethylbenzyl)diphenylamine are preferred as amine-based antioxidants with a pKa of less than 7.

[0052] <Phosphorus-based antioxidants> Examples of phosphorus-based antioxidants include triphenyl phosphite, triphenyl phosphate, tris(2-ethylhexyl) phosphite, diphenyl monodecyl phosphite, tetraphenyldipropylene glycol diphosphite, triethyl phosphite, tris(2,4-di-tert-butylphenyl) phosphite, nitrilotris(methylphosphonic acid), 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide, and bis(2,4-di-tert-butyl-6-methylphenyl)ethyl phosphite. From the viewpoint of compatibility with other components in the absorption solution, triphenyl phosphite, tris(2-ethylhexyl) phosphite, diphenyl monodecyl phosphite, tetraphenyldipropylene glycol diphosphite, triethyl phosphite, and nitrilotris(methylphosphonic acid) are preferred as phosphorus-based antioxidants.

[0053] The antioxidant content in the acidic gas absorbent of this embodiment is 0.05 to 20.0% by mass, preferably 0.1 to 10.0% by mass, and more preferably 0.1 to 5.0% by mass. By keeping the antioxidant content within the above range, the carbon dioxide absorption capacity remains good even after the acidic gas absorbent is exposed to an oxidizing atmosphere or high-temperature environment. Two or more antioxidants may be combined, and a combination of an amine-based antioxidant with a pKa of less than 7 and a phosphorus-based antioxidant is preferred. If a phenol-based antioxidant is included as an antioxidant, the content of the phenol-based antioxidant is preferably 0.1 to 5.0% by mass. If a sulfur-based antioxidant is included as an antioxidant, the content of the sulfur-based antioxidant is preferably 0.1 to 5.0% by mass. When an amine-based antioxidant with a pKa of less than 7 is included as an antioxidant, the content of the amine-based antioxidant with a pKa of less than 7 is preferably 0.05 to 20.0% by mass, more preferably 0.1 to 10.0% by mass, and even more preferably 0.1 to 5.0% by mass. When a phosphorus-based antioxidant is included as an antioxidant, the content of the phosphorus-based antioxidant is preferably 0.05 to 20.0% by mass, more preferably 0.1 to 10.0% by mass, and even more preferably 0.1 to 5.0% by mass.

[0054] (Composition and Uses of Acidic Gas Absorbent Solution) From the viewpoint of good carbon dioxide absorption capacity, the acidic gas absorbent solution preferably contains 5.0 to 90.0% by mass of oxygen-containing polymer. From the viewpoint of good carbon dioxide absorption capacity, the acidic gas absorbent solution preferably contains 10.0 to 95.0% by mass of amine compound.

[0055] From the viewpoint of good carbon dioxide absorption capacity, the content of the oxygen-containing polymer is preferably 5.0% by mass or more, more preferably 15.0% by mass or more, even more preferably 20.0% by mass or more, and also preferably 90.0% by mass or less, more preferably 80.0% by mass or less, even more preferably 70.0% by mass or less, and particularly preferably less than 70.0% by mass.

[0056] From the viewpoint of good carbon dioxide absorption capacity, the amine compound content is preferably 10.0% by mass or more, more preferably 15.0% by mass or more, even more preferably 20.0% by mass or more, and also preferably 95.0% by mass or less, more preferably 90.0% by mass or less, and even more preferably 85.0% by mass or less.

[0057] The acidic gas absorbent may optionally contain additives such as corrosion inhibitors and viscosity modifiers, within limits that do not hinder the effects of the present invention. The total content of other components (additives) in the acidic gas absorbent is not particularly limited, but is preferably 20.0% by mass or less, more preferably 10.0% by mass or less, particularly preferably 5.0% by mass or less, and may be 0% by mass. The water content in the acidic gas absorbent is not particularly limited, but is preferably 5% by mass or less, more preferably 3.0% by mass or less, particularly preferably 2.0% by mass or less, and may be 0% by mass.

[0058] [Method for producing acidic gas absorbent solution] The acidic gas absorbent solution of this embodiment can be produced by mixing the above-mentioned oxygen-containing polymer, an amine compound with a pKa of 7 or higher, and an antioxidant. Alternatively, the above-mentioned additives and water may be added and mixed as needed.

[0059] In the method for producing the acidic gas absorbent of this embodiment, it is preferable to obtain the acidic gas absorbent by stirring and mixing the above-mentioned oxygen-containing polymer, an amine compound with a pKa of 7 or higher, and an antioxidant under a nitrogen atmosphere at 10 to 60°C. The stirring and mixing method is not particularly limited and can be carried out using known means.

[0060] The mixing temperature is preferably 10 to 60°C, more preferably 20 to 40°C, from the viewpoint of preventing the volatilization of the amine compound. The atmosphere during mixing is preferably a nitrogen atmosphere, from the viewpoint of preventing water from entering the absorbent and suppressing oxidative degradation. Nitrogen may be introduced into either the gas phase or the liquid phase. When introducing nitrogen into the liquid phase, it is preferable to use a lower flow rate than when introducing it into the gas phase, from the viewpoint of suppressing the volatilization of the amine compound.

[0061] The acidic gas absorbent of this embodiment is suitable for acidic gas recovery and separation processes, and is particularly suitable for carbon dioxide recovery and separation processes when the acidic gas is carbon dioxide. Examples of carbon dioxide recovery and separation processes include contacting a gas containing carbon dioxide with an acidic gas absorbent to selectively absorb and separate the carbon dioxide, releasing and recovering the carbon dioxide by heating or depressurizing the liquid that has absorbed the carbon dioxide, and recovering the liquid after the carbon dioxide has been released to regenerate it as an acidic gas absorbent.

[0062] There are no particular restrictions on the temperature of the absorbent liquid when absorbing carbon dioxide with the acidic gas absorbent liquid, but from the viewpoint of suppressing the load of gas cooling energy, it is preferably -10 to 60°C, more preferably 0 to 50°C. If it is above the lower limit of the above range, the load of gas cooling energy can be suppressed, and if it is below the upper limit of the above range, carbon dioxide can be absorbed sufficiently. There are no particular restrictions on the gas pressure when absorbing carbon dioxide with the acidic gas absorbent liquid, but if it is assumed to be about the same as the partial pressure of carbon dioxide in the atmosphere, from the viewpoint of making it easier to separate and recover carbon dioxide using the pressure difference from the atmosphere, it is preferably 20 to 100 Pa, more preferably 30 to 80 Pa, and particularly preferably 32 to 65 Pa. If it is assumed to be about the same as the partial pressure of carbon dioxide in combustion exhaust gas, from the viewpoint of making it easier to reduce the amount of water absorbed and to separate and recover carbon dioxide, it is preferably 0.5 to 100 kPa, more preferably 1 to 50 kPa, and particularly preferably 3 to 30 kPa.

[0063] There are no particular restrictions on the temperature of the absorbent liquid when releasing carbon dioxide from the acidic gas absorbent liquid, but it is preferably 50 to 120°C, more preferably 70 to 100°C, and most preferably 70 to 90°C. If the temperature is above the lower limit of the above range, carbon dioxide can be sufficiently desorbed from the acidic gas absorbent liquid, and if it is below the upper limit of the above range, deterioration of the acidic gas absorbent liquid can be suppressed. There are no particular restrictions on the gas pressure when releasing carbon dioxide from the acidic gas absorbent liquid, but from the viewpoint of facilitating the separation and recovery of carbon dioxide using the pressure difference from the atmosphere, it is preferably 0.5 to 20 Pa, more preferably 2 to 20 Pa, and most preferably 2.5 to 15 Pa.

[0064] The temperature difference between the absorption of carbon dioxide into the acidic gas absorbent and its release from the acidic gas absorbent is set by comparing and balancing the thermal energy required for carbon dioxide release with the amount recovered, preferably 80°C or less, more preferably 60°C or less. By combining this with processes such as hydrogen stripping or heat pumps, the temperature difference can be reduced, thereby lowering the required energy.

[0065] [Method for Reducing Acidic Gases] In the acidic gas reduction method of this embodiment, the amount of carbon dioxide in the gas is reduced by bringing the acidic gas absorbent liquid of this embodiment into contact with a gas containing carbon dioxide. The acidic gas absorbent liquid of this embodiment is effective not only when recovering carbon dioxide from a gas that does not contain water, but also when recovering carbon dioxide from a gas containing both carbon dioxide and water, as it can separate and remove water without heating and evaporation, thus further reducing the energy required to recover acidic gases from the gas.

[0066] Contact between the acidic gas absorbent and the gas can be achieved, for example, by adding the acidic gas absorbent to the gas, by continuously circulating the gas through a container filled with the acidic gas absorbent, or by filling a container filled with the acidic gas absorbent with the gas. To improve the contact efficiency between the acidic gas absorbent and the gas, methods such as providing a packing material in the container, spraying the acidic gas absorbent onto the gas, or bubbling the gas into the acidic gas absorbent can also be used.

[0067] The present invention will be described in detail below based on the following examples, but the present invention is not limited to the following examples, and various modifications are possible without departing from the spirit of the invention.

[0068] [Synthesis of Oxygen-Containing Polymers] (Synthesis Example 1) In a reactor equipped with a stirring blade, a distillate trap, and a pressure regulator, 6520 g of propylene oxide was polymerized using 480 g of n-butanol as an initiator in the presence of a potassium hydroxide (KOH) catalyst. After neutralization and removal of the neutralized salt, a monofunctional PPG (polymer A) with a number average molecular weight of 1283 was obtained. 5000 g of polymer A was charged into a reactor equipped with a stirring blade, a distillate trap, and a pressure regulator. Next, a 28% by mass sodium methoxide (NaOMe) methanol solution was added so that the amount of NaOMe was 1.1 moles per mole of hydroxyl groups of polymer A. After heating to 70°C, nitrogen was introduced and methanol was removed by atmospheric pressure distillation. Subsequently, the temperature was raised to 130°C and stirred and mixed under reduced pressure of -0.1 MPaG for 4 hours to remove methanol by distillation, converting polymer A to sodium alkoxide. Next, after cooling to 100°C, 1.1 moles of methyl chloride were sequentially added at a rate of 400 g / hr per mole of sodium in the sodium alkoxide, and the mixture was reacted at 100°C for 2 hours. Then, the mixture was stirred and mixed for 0.5 hours at 100°C under reduced pressure of -0.1 MPaG, and the unreacted methyl chloride was removed by distillation under reduced pressure to obtain a crude product in which the hydroxyl groups of polymer A were methoxylated. Next, 2500 g of distilled water was added to the reactor and stirred and mixed for 15 minutes to separate the oil and water from the neutralized salt. Only the oil layer was extracted, and 4 parts by mass of adsorbent were added to 100 parts by mass of the oil layer, and the mixture was heated to 120°C and stirred and mixed for 1.5 hours under reduced pressure of -0.1 MPaG. By filtering the adsorbent, polypropylene glycol butyl methyl ether (PPG1), a terminally methylated derivative of polymer A with a number average molecular weight of 1283, was obtained.

[0069] (Synthesis Example 2) Polypropylene glycol dimethyl ether (PPG2) with a number average molecular weight of 1570 was obtained in the same manner as in Synthesis Example 1, except that the initiator was changed to methanol and the amount of propylene oxide polymerized was changed.

[0070] (Synthesis Example 3) In a reactor equipped with a stirring blade, distillate trap, and pressure regulator, 5600 g of propylene oxide was polymerized with 400 g of methanol as an initiator in the presence of a potassium hydroxide (KOH) catalyst. After neutralization and removal of the neutralized salt, polypropylene glycol monomethyl ether (PPG3) with a number average molecular weight of 545 was obtained.

[0071] (Synthesis Example 4) Polypropylene glycol dimethyl ether (PPG4) with a number average molecular weight of 1797 was obtained in the same manner as in Synthesis Example 2, except that the amount of propylene oxide polymerized was changed.

[0072] (Synthesis Example 5) Polypropylene glycol dimethyl ether (PPG5) with a number average molecular weight of 786 was obtained in the same manner as in Synthesis Example 2, except that the amount of propylene oxide polymerized was changed.

[0073] [Preparation of Acid Gas Absorbent Solution] An acid gas absorbent solution was prepared using the oxygen-containing polymer, amine compound, and antioxidant shown below.

[0074] <Oxygen-containing polymers> ・PPG1: Produced in Synthesis Example 1. ・PPG2: Produced in Synthesis Example 2. ・PPG3: Produced in Synthesis Example 3. ・PPG4: Produced in Synthesis Example 4. ・PPG5: Produced in Synthesis Example 5. ・DPG: Dipropylene glycol

[0075] <Amine Compounds> ・DBAPA: 3-(dibutylamino)propylamine (pKa = 10.2) (manufactured by Tokyo Chemical Industry Co., Ltd.) ・DHA: Dihexylamine (pKa = 11.3) (manufactured by Tokyo Chemical Industry Co., Ltd.) ・DBZA: Dibenzylamine (pKa = 8.8) (manufactured by Tokyo Chemical Industry Co., Ltd.) ・BAE: 2-(butylamino)ethanol (pKa = 14.8) (manufactured by Tokyo Chemical Industry Co., Ltd.) ・4-Ethylaniline (pKa = 5.1) (manufactured by Tokyo Chemical Industry Co., Ltd.)

[0076] <Antioxidants> ・DCD: 4,4'-bis(α,α-dimethylbenzyl)diphenylamine (Product name: Nonflex DCD) (Manufactured by Seiko Chemical Co., Ltd.) ・TP: Triphenyl phosphite (Manufactured by Tokyo Chemical Industry Co., Ltd.) ・JPM-311: Diphenyl monodecyl phosphite (Manufactured by Johoku Chemical Industry Co., Ltd.) ・JPP-100: Tetraphenyldipropylene glycol diphosphite (Manufactured by Johoku Chemical Industry Co., Ltd.) ・ADF: Octylated diphenylamine (Product name: Nocrac AD-F) (Manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) ・1520L: 4,6-bis(octathiomethyl)-o-cresol (Product name: Irganox 1520L) (Manufactured by BASF) • 1076: Octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (product name: Irganox 1076) (manufactured by BASF) • T2E1HP: Tris(2-ethylhexyl)phosphite (manufactured by Tokyo Chemical Industry Co., Ltd.)

[0077] (Example 1) 50 g of PPG1, 50 g of DBAPA, 0.03 g of DCD, and 0.03 g of TP were placed in a 300 mL flask equipped with a stirring blade, and the mixture was stirred at 25°C for 1 hour under a nitrogen atmosphere to produce an acidic gas absorption solution.

[0078] (Examples 2-49) The oxygen-containing polymer, amine compound, and antioxidant used were changed to the respective formulations shown in Examples 2-49 of Tables 1-8, and acidic gas absorbents were prepared in the same manner as in Example 1. The appearance of the acidic gas absorbents obtained in Examples 1-49 was all colorless to yellowish transparent.

[0079] [Performance Evaluation of Acidic Gas Absorbents] <Evaluation 1> For each of the acidic gas absorbents in Examples 1 to 35, carbon dioxide (CO2) was evaluated as follows: ２) Absorption performance evaluation was performed. 100 g of the acidic gas absorbent was charged into a 0.5 L square steel can, a crown cap and a protector were set with the inner lid removed, and the can was heated in an oven at 90°C for 144 hours in the atmosphere (accelerated test). This accelerated test reproduces both oxidation due to atmospheric oxygen and deterioration due to high temperature. 5 g of the acidic gas absorbent after the accelerated test was placed into a 100 mL glass bottle, and a stirring bar was added. The glass bottle was placed into a bell jar in an open state and set on a magnetic stirrer. CO ２ A gas cylinder and the bell jar were connected, at a rotation speed of 300 min －１ , CO ２ at a CO gas flow rate of 0.3 L / min, CO ２ gas was introduced into the bell jar. The CO content of the acidic gas absorbent after 10 minutes ２ absorption amount was calculated by the following formula. CO ２ Absorption amount [mg / g] = (CO ２ Total weight of glass bottle after gas introduction [mg] - CO ２ Total weight of glass bottle before gas introduction [mg]) / Amount of acidic gas absorbent [g] This test was performed three times for each acidic gas absorbent, and the three CO ２ the average value of absorption amounts was defined as the CO absorption amount per 1 g of acidic gas absorbent ２ absorption amount. The CO absorption amount per 1 g of acidic gas absorbent after the accelerated test ２ when the absorption amount was 30.0 mg / g or more, it was judged that the CO ２ absorption performance was good. Tables 1 to 5 show the CO ２ absorption performance evaluation results of Examples 1 to 35.

[0080]

[0081] Table 1 shows examples in which the content of the antioxidant in the acidic gas absorbent was changed. Examples 1 to 7 are working examples, and Example 8 is a comparative example. It was confirmed that the acidic gas absorbents containing an oxygen-containing polymer, an amine compound having a predetermined pKa, and a predetermined amount of antioxidant (Examples 1 to 7) have superior carbon dioxide absorption capacity after the accelerated test as compared with Example 8, which does not contain the predetermined amount of antioxidant.

[0082]

[0083] Table 2 shows the evaluation results when the content of oxygen-containing polymer and amine compound in the acidic gas absorbent solution was changed. Examples 9, 11, 13, and 15 are examples, and examples 10, 12, 14, and 16 are comparative examples. An acidic gas absorbent solution (Example 9) containing an oxygen-containing polymer, an amine compound having a predetermined pKa, and a predetermined amount of antioxidant was found to have superior carbon dioxide absorption capacity after accelerated testing compared with Example 10, which did not contain the predetermined amount of antioxidant. Similar effects can be confirmed by comparing Examples 11 and 12, 13 and 14, and 15 and 16.

[0084]

[0085] Table 3 shows the evaluation results when the type of antioxidant in the acidic gas absorbent solution is changed. Examples 17-19 are examples, and Example 20 is a comparative example. Acidic gas absorbent solutions (Examples 17-19) containing an oxygen-containing polymer, an amine compound having a predetermined pKa, and a predetermined amount of antioxidant were found to have superior carbon dioxide absorption capacity after accelerated testing compared to Example 20, which did not contain a predetermined amount of antioxidant.

[0086]

[0087] Table 4 shows the evaluation results when the types of oxygen-containing polymers and amine compounds in the acidic gas absorbent solution are changed. Examples 21, 23, 25, 26, 28, and 30 are examples, and examples 22, 24, 27, 29, and 31 are comparative examples. An acidic gas absorbent solution (Example 21) containing an oxygen-containing polymer, an amine compound having a predetermined pKa, and a predetermined amount of antioxidant was found to have superior carbon dioxide absorption capacity after accelerated testing compared with Example 22, which did not contain a predetermined amount of antioxidant. Similar effects can be confirmed by comparing Examples 23 with Example 24, Examples 25 and 26 with Example 27, Examples 28 with Example 29, and Examples 30 with Example 31.

[0088]

[0089] Table 5 shows examples of acidic gas absorbents that do not contain amine compounds with a pKa of 7 or higher. Examples 32-35 are comparative examples. Acidic gas absorbents that do not contain amine compounds with a pKa of 7 or higher (Examples 32-35) showed CO2 levels after accelerated testing. ２The absorption rate was less than 30 mg / g, indicating that the carbon dioxide absorption capacity after accelerated testing was insufficient.

[0090] <Evaluation 2> For each acidic gas absorbent in Examples 36-45, CO ２ Absorption performance was evaluated. 80 g of acidic gas absorbent solution was placed in a 0.5 L steel square can. With the inner lid removed, the crown cap and protector were attached, and the can was heated in an oven at 90°C in the atmosphere for 168 hours (accelerated test). This accelerated test reproduces both oxidation by oxygen in the atmosphere and degradation by high temperature. 5 g of the acidic gas absorbent solution after the accelerated test was placed in a 100 mL glass bottle, and a stirring bar was added. This glass bottle, with the opening facing outwards, was placed in a bell jar and positioned on a magnetic stirrer. CO ２ Connect the gas cylinder and bell jar, and set the rotation speed to 300 mins. －１ CO ２ With a gas flow rate of 0.3 L / min, CO2 enters the bell jar. ２ Gas was introduced. Regarding the acidic gas absorbent solution after 10 minutes, １３ In 13C nuclear magnetic resonance (NMR) analysis, carbamates (amines and CO2) appear around 160 ppm. ２ From the cumulative area of ​​the peaks of the reactants, CO ２ The absorption amount [mol / g] was determined. If a new peak due to oxidative degradation was detected near the carbamate peak and interfered, the cumulative area was calculated from the position of the minimum between the carbamate peak and the new peak. ２ From the amount absorbed, CO is calculated using the following formula. ２ Loading (CO per amine molecule) ２ The amount of CO absorbed was calculated. ２ Loading = CO ２ Absorption amount [mol / g] / Total amount of amine in acidic gas absorbent solution [mol / g] Tables 6 and 7 show the CO2 values ​​for Examples 36-45. ２ The results of the absorption performance evaluation are shown below.

[0091]

[0092] Table 6 shows the evaluation results when accelerated testing was performed on combinations of PPG1, DHA, DCD, and TP. Examples 36 and 37 are examples, and Example 38 is a comparative example. Example 39 is a CO2 test performed without accelerated testing. ２ This is a reference example of what happens when CO is absorbed. Comparing Example 38 and Example 39, it can be seen that accelerated testing is performed. ２ Although the absorption performance deteriorates, it was confirmed that the acidic gas absorbent containing a predetermined amount of antioxidant (Examples 36 and 37) suppressed the decrease in carbon dioxide absorption capacity after accelerated testing.

[0093]

[0094] Table 7 shows the evaluation results when the antioxidant was changed in the combination of PPG5 and DHA. Examples 40 to 44 are examples, and Example 45 is a comparative example. Acidic gas absorbents (Examples 40 to 44) containing an oxygen-containing polymer, an amine compound having a predetermined pKa, and a predetermined amount of antioxidant were found to have superior carbon dioxide absorption performance after accelerated testing compared to Example 45, which did not contain a predetermined amount of antioxidant.

[0095] <Evaluation 3> For each of the acidic gas absorbents in Examples 46-49, the same evaluation as in Evaluation 2 was used, except that the heating time in the accelerated test was set to 240 hours. ２ Loading was requested.

[0096]

[0097] Table 8 shows the evaluation results when the amount of antioxidants (DCD and TP) is changed in the combination of PPG5 and DHA. Examples 46 to 48 are examples, and Example 49 is a comparative example. Acidic gas absorbents (Examples 46 to 48) containing an oxygen-containing polymer, an amine compound having a predetermined pKa, and a predetermined amount of antioxidant were found to have superior carbon dioxide absorption capacity after accelerated testing compared to Example 49, which did not contain a predetermined amount of antioxidant.

Claims

1. An acidic gas absorbent comprising an oxygen-containing polymer, an amine compound with a pKa of 7 or higher, and an antioxidant, wherein the antioxidant content is 0.05 to 20.0% by mass.

2. The acidic gas absorbent according to claim 1, wherein the content of the oxygen-containing polymer is 5.0 to 90.0% by mass.

3. The acidic gas absorbent according to claim 1, wherein the content of the amine compound is 10.0 to 95.0% by mass.

4. The acidic gas absorbent according to claim 1, wherein the amine compound is a compound having one primary amino group or a secondary amino group.

5. The acidic gas absorbent according to claim 1, wherein the antioxidant is at least one selected from the group consisting of phenolic antioxidants, sulfur-based antioxidants, amine-based antioxidants having a pKa of less than 7, and phosphorus-based antioxidants.

6. The acidic gas absorbent according to claim 5, wherein the antioxidant comprises at least one selected from the group consisting of the phenolic antioxidant and the amine antioxidant, and at least one selected from the group consisting of the sulfuric antioxidant and the phosphorus antioxidant.

7. The acidic gas absorbent according to claim 5, wherein the antioxidant comprises the sulfur-based antioxidant.

8. The acidic gas absorbent according to claim 1, wherein the oxygen-containing polymer has at least one group selected from the group consisting of oxyalkylene groups, carbonate groups, and ester groups.

9. The acid gas absorbent according to claim 1, for use in an acid gas recovery and separation process.

10. A method for reducing acidic gases, comprising contacting an acidic gas absorbent liquid according to any one of claims 1 to 9 with a gas containing carbon dioxide to reduce the amount of carbon dioxide in the gas.

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